title: Differences between X-ray and MRI-determined knee cartilage thickness in weight-bearing and non-weight-bearing conditions.
abstract: OBJECTIVE
  Determine the effect of loading upon MRI-based mean medial femorotibial cartilage thickness (mMFT_th) and radiograph-based minimum joint space width (mJSW), and determine loading's effect on the relationship between these measures.
  
  
  METHODS
  MRI and radiographs were analyzed of 25 knees in weight-bearing and non-weight-bearing conditions. Eight subjects had a Kellgren-Lawrence (KL) grade of 0, indicating no evidence of radiographic OA. The rest were KL = 2 or KL = 3, indicating mild to moderate OA. The change from unloaded to loaded conditions was calculated.
  
  
  RESULTS
  Joint space measures decreased from unloaded to loaded conditions for both radiographs (mJSW = 3.29 mm unloaded to 3.16 mm loaded, P < 0.05) and MRI (mMFT_th = 2.70 mm unloaded to 2.55 mm loaded P < 0.001). The mean absolute difference measured from radiographs was larger for the OA group than the control group, at -0.20 mm for OA vs +0.01 mm for control. Loaded X-ray and loaded MRI joint space values from our study were no better correlated to one another than loaded X-ray and unloaded MRI.
  
  
  CONCLUSIONS
  Knee loading does not add a very significant value to the study of joint space on healthy knees, but loading may play a role in the study of OA knees. Unloaded MRI assessments of cartilage thickness are as correlated to loaded JSW as to loaded MRI measurements. More study is necessary to determine whether loaded MRI adds significant value to the study of OA progression.
authors.affiliation: Musculoskeletal and Quantitative Imaging Group (MQIR), Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, USA. Electronic address: Megan.Marsh@ucsf.edu.
authors.forename: M
authors.initials: M
authors.lastname: Marsh
authors.forename: R B
authors.initials: RB
authors.lastname: Souza
authors.forename: B T
authors.initials: BT
authors.lastname: Wyman
authors.forename: M-P
authors.initials: MP
authors.lastname: Hellio Le Graverand
authors.forename: K
authors.initials: K
authors.lastname: Subburaj
authors.forename: T M
authors.initials: TM
authors.lastname: Link
authors.forename: S
authors.initials: S
authors.lastname: Majumdar
mesh_terms: D002358:Cartilage, Articular / Q000000981:diagnostic imaging / Q000473:pathology* / Q000502:physiology; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000473:pathology* / Q000502:physiology; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009929:Organ Size; D020370:Osteoarthritis, Knee / Q000000981:diagnostic imaging / Q000473:pathology*; D011859:Radiography; D016474:Weight-Bearing
keywords: Cartilage thickness; Joint space width; Knee; MRI; Osteoarthritis; Radiograph